112 Miscellaneous, 



There is thus formed in the connective tissue a series of regular 

 glandular sacs, adhering one to another. On teasing out the tissues 

 of the living animal it is seen that these gland-cells attain consider- 

 able dimensions, and that the globules arc formed at the expense of 

 their granular protoplasm. The globules originate and grow in 

 vacuoles, which become successively hollowed out in the protoplasmic 

 mass, so that finally the cells are nothing more than transparent 

 masses formed by an agglomeration of little delicate-walled alveoli 

 enclosing the globules. The latter, on being set free, probably by 

 simple rupture, emerge at the bottom of the groove, where they 

 attach themselves to the fine organic membrane secreted by the 

 epithelium. 



The calcareous and mucous glands are absent, as stated by 

 Lcydig*, in all the parts covered by the shell, and I was able to 

 prove that the calcareous gland.s of the collar, conformably to the 

 opinion of Semper, do not contribute in any way to the formation 

 of the test. 



The only elements which take part in the production of the 

 latter are, commencing from in front: — (1) The paUial groove, 

 where is formed the epidermis with the glandular sacs, which pro- 

 duce the globules, and the existence and function of which I believe 

 I am the first to describe ; (2) the bandelet, or pallial gland, on 

 which appears to devolve the secretion of the calcareous matter ; 

 (3) the pallial epithelium foUowiug the bandelet, which provides 

 the shell with its pigment and completes its calcification by the 

 deposition of organo-calcareous layers, homologous to the layers of 

 nacre in the Pelecypods. 



I determined, moreover, that, when the animal has attained its 

 fall size, the bandelet and the glands ivith globules have comj^htely 

 disappeared. 



It is only the epithelium of the mantle and of the pulmonary sac 

 which retains its activity, for the purpose of contributing to the 

 internal thickening of the test, and also of replacing the loss of 

 portions of it, as is shown by the following experiment, which 

 indicates the rapidity and activity of the secretion. 



If we lay bare a portion of the surface of the pulmonary sac, 

 by removing a fragment of the shell, it is possible even at the end 

 of an hour and a half to two hours to detach an extremely delicate 

 organic membrane, covering the whole surface, and strewn with 

 rhombohcdral and radiating crystals of carbonate of lime. If 

 allowed to remain, this membrane thickens very rapidly, and finally 

 closes up the opening with a solid calcareous wall. 

 " In no case (contrary to the statement of C. Picard t) does the 

 mucus ])roduced by the collar or the mouth take part in this pro- 

 cess of re])aration. 



As regards the activity of the pallial epitlu'lium, it is such that, 

 during two consecutive months, I was able to observe animals, 

 which were deprived of food, reproducing every day the organo- 

 calcareous membrane which I removed every morning. — Compttfs 

 liendas, tome cxlii, no. 7 (August 17, ISDl), pp. 317-311). 



* Tjoydig, ' Die llautilocko and Schalo dor Gastropodon.' 



t Dr. C. Picar.l. ' 1114. dos .Moll. torr. et tiiiv. (jui vivent dans le 

 dJpaitoiUf^ut de la S mr.ao,' Ir^Jd. 



